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I live in Georgia (around the Atlanta area) and recently discovered mold in the crawl space of my home (I plan to have the mold professionally removed). My crawl space is about 30' by 15' (4' to 15' in height) in size and is vented. The ceiling of the crawl space has fiberglass batts that are starting to fall from moisture and rodents. The mold is forming on the wood where the batts are installed.

The crawl space has no duct work or machinery in it. It is a open space with a couple of wires, an AC condensation line, and the water main pipe running through it. I have not noticed any significant wanter build up inside, so I don't think a drain system is needed.

I was thinking of encapsulating (floor and walls) the space myself using 10 mil plastic sheeting, foam board, and calk.

My questions are, is encapsulation over kill? Is encapsulating recommended in high humidity areas? Do I need to reinsulate the ceiling if I encapsulate? Do I need a permeant dehumidifier in the space if i encapsulate, or would a temporary dehumidifer be ok just to dry the area after encapsulation?

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2 Answers

You didn't say that there is plastic on the crawl space floor/dirt. So, I suggest you cover it in plastic first. Then I suggest you just put a cheap box fan (or two) down there to circulate the air. That's what I do to keep the moisture level down in my crawl space in Summerville, SC. I just run the fan during the summer months. I have AC ducts in my crawl space and their insulation drips water without the fan. I did a lot of research on encapsulation, and decided it was way too costly, without clear benefits. But, unlike your situation, I never have had mold, just water. I kind of came to the conclusion that there are a lot of folks making a buck on encapsulation. Try the plastic and fans approach first. It's cheap compared to encapsulation and may be all you need.

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Your situation is not uncommon.

Here's a study on crawl space encapsulation in the Southeast USA: http://aceee.org/files/proceedings/2004/data/papers/SS04_Panel1_Paper07.pdf (Moisture Solution Becomes Efficiency Bonanza in Southeastern United States Bruce Davis and Cyrus Dastur, Advanced Energy #DE-FC26-00NT40995 ). And see also What are the pros and cons of a vented vs unvented crawl space?

Don't do the walls with anything impermeable: you'll trap moisture in the space which is worse than doing nothing. Do consider doing the floor. Using bubble wrap below the floor can reduce tearing of the plastic. Note that some people worry about plastic leading to mold growth below the plastic: thus an effort to completely seal the ground.

You should get a humidity meter (they are not expensive) and monitor before and after. Report back with measured humidity levels now and it might help refine the answer.

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